1. Field of the Invention
This invention relates generally to the field of guidance systems for gun-fired munitions, missiles and high-speed flying objects. More particularly, it pertains to methods of integrating guidance control and navigation sensors that do not use signals from a Global Positioning System and do not use inertia components. Methods described herein, when appropriately integrated onto guided munitions, directly measure the angular orientation of the munition with reference to a specific point. Advantageously, the measurement is precisely performed in real-time and is free of measurement drift errors.
Importantly, the novel concepts described herein can be incorporated into a new class of sensors that can become an important component for guidance systems that do not require the Global Positioning System (GPS) and can be used for the precise tracking of a munition in-flight and homing into targets. Because this new class of sensors can be made in micro sized cavities, they enable the precise control of small caliber munitions, which is currently not possible with existing technologies. In addition to its applicability to munitions, this new class of sensors may improve control and maneuverability of robotic systems, automated machinery and other systems that employ angle and position measurement.
2. Background of the Invention
Precision-guided munitions are self-guiding weapons intended to precisely hit a target with minimum “collateral damage”. Because the damage effects of an explosive weapon scale with distance, improvements in accuracy (and hence reduction in miss distance) enables a target to be effectively attacked with fewer and/or smaller munitions.
Precision sensors that determine position and orientation information are essential for closing the feedback guidance and control loop in all smart and guided projectiles such as munitions and missiles. Orientation measurement sensors are particularly essential in gun-fired munitions since they also provide the means to significantly reduce the guidance actuation authority and related power consumption levels, thereby minimizing the need to allocate a considerable amount of the munitions's volume to actuation mechanisms and their power sources.
Together with precision, future sensors for guidance need to provide information in real time, and exhibit very fast acquisition of position information for the round in flight. This is particularly true when discrete firing thrusters are used for tracking and/or course correction since, with such actuation mechanisms, only a limited number of corrective actions are available and they can be effectively used only if the full angular orientation of the munition is known at all times and is used to properly time thruster firing.
Consequently, improvements made to the guidance of precision-munitions is of particular importance.
Present day guidance systems typically use inertial or magnetometer-based systems as a means to sense orientation and position of an object in flight. A typical inertial navigation system uses a combination of accelerometers and solves a large set of differential equations to estimate position and attitude, when starting from a known initial position.
Current sensors for the measurement of the angular position of one object relative to another can be divided into the following three major categories. A first category of sensors measure changes in the angular position using inertial devices such as accelerometers and gyros. Inertial based angular position sensors, however, suffer from drift and noise error accumulation problems because the drift and the measurement errors are accumulated over time and the acceleration has to be integrated twice to determine the angular position. Consequently drift errors reach intolerable levels, particularly as a munitions's range is increased.
Another problem associated with inertia based angular position sensors is that the angular position of one object relative to another cannot be measured directly, i.e., the orientation of each object relative to the inertia frame has to be measured separately and used to determine their relative angular position. Since both measurements contain drift errors, the relative angular position measurement compounds the problem even more.
A second class of angular position sensors operate using optical methods. Unfortunately however, these optical, angular position sensors require a line of sight between two objects and have a limited range to perform the measurement. In general, optical angular position sensors and methods have a limited range of angular position measurement and require relatively high amount of power to operate. As a result, they are largely employed with ground equipment or stations, and seldom onboard of gun-fired munitions.
A third category of angular orientation measurement systems use radio frequency (RF) antennas printed or placed on the surface of an object to reflect RF energy emanating from a ground-based radar system. The reflected energy is then used to track the object on its way to a destination. With two moving objects, the radar measures the time difference between the return signals from each of the objects and thereby determines angular information in terms of the angle that the relative velocity vector makes with respect to a coordinate system fixed to one of the objects.
With such systems, measurement of full spatial orientation of an object (relative to the fixed radar or a second object) is very difficult. In addition, the information about the object orientation is determined at a radar station and has to be transmitted to the moving object(s) if it is to be used for course correction. In addition, it is also very difficult and costly to develop systems that could track multiple projectiles.
Finally, it is worth noting that in addition to the above angular orientation measurement systems, GPS signals have been used to provide angular orientation information. Such systems however, are prone to jamming and to the loss of signal, particularly in munitions applications.
The next generation of guidance control and navigation systems should therefore minimize any dependency on the Global Positioning System (GPS) or inertial technologies. They should also exhibit low cost. Such systems will undoubtedly find applicability to robotics and automation in addition to the precise targeting of munitions.
Fortunately however, alternative technologies are being developed which offer the promise of providing a type of angular position sensors suitable for the above-noted uses. In particular, C. Pereira, Q. J. Ge and J. Rastegar described such sensors in a paper entitled “On the Geometry of 3D Orientation Measurement Using a New Class of Wireless Angular Position Sensors”, that appeared in the Proceedings of DETC'03, 2003 ASME Design Engineering Technical conferences and Computers and Information in Engineering Conferences which was held in Chicago, Ill. on Sep. 2-3, 2003.
In that paper, the authors therein described a new class of wireless angular position sensors that comprised waveguides that receive and record electromagnetic energy emitted by a polarized RF source. The angular position of the waveguide is indicated by the energy level. A system equipped with multiple waveguides is used as a 3D orientation sensor.
Given their potential for providing a significant advance in the art of munitions and other navigation systems, position sensors employing waveguides are of particular interest. Such position sensors are the subject of the present invention.